The present invention relates generally to differential gear mechanisms, and more particularly, to such mechanisms of the type commonly referred to as "locking differentials".
Differential gear mechanisms of the type to which the present invention applies are broadly referred to as "limited slip differentials" and typically include a clutch pack which is operable to limit or retard differentiating action between the output gears (side gears). More specifically, however, the present invention is intended for use on limited slip differentials of the type referred to as "locking differentials", and will be described in connection therewith. In a locking differential, means are provided for engaging or locking the clutch set, rather than permitting it to slip, to substantially reduce the amount of differentiating action permitted between the side gears.
Locking differentials of various types are now generally well known in the art, including both interaxle lockers, and inter-wheel lockers. Inter-wheel locking differentials may be applied either to conventional rear-wheel drive vehicles, or to the more recent front-wheel drive vehicles. Although the present invention may be utilized to advantage in any of the above-described types of locking differential, it is especially advantageous when applied to an inter-wheel, front-wheel drive vehicle, and will be described in connection therewith.
As is now quite well known to those involved in the design of front-wheel drive vehicles, especially the "compact" and "subcompact" automobiles, one of the major problems involves the limited amount of space available for the various engine and drive train components and accessories. The lack of space becomes especially difficult in the case of a component which is "optional" to the vehicle purchaser, and which is larger than the standard component being replaced. Such is the case with a locking differential replacing a conventional, open differential.
In the case of a locking differential, the space problem is compounded by the dimensional limitations imposed in regard to both the axial length and the gear case outside diameter. For example, because of the location of the surrounding components and accessories, there may be a specified maximum "bearing span", i.e., the axial distance between the two sets of bearings which provide rotational support for the locking differential mechanism, relative to the main, outer casing. At the same time, the location of adjacent components may result in a specified maximum casing diameter, over at least a major portion of the axial extent of the locking differential. In the prior art locking differentials of the type including an actuating means for locking up the clutch set, such as is illustrated in U.S. Pat. No. Re. 28,004, assigned to the assignee of the present invention, the clutch set has typically been disposed axially from one of the side gears. In such an arrangement, the side gear and a cam member disposed between the side gear and the clutch set define cooperating cam surfaces, such that retarding rotation of the cam member relative to the side gear causes axial movement of the cam member, locking the clutch set and minimizing differentiating action. However, such an arrangement results in a locking differential unit which would substantially exceed the "bearing span" available in front-wheel drive applications.
Accordingly, it is an object of the present invention to provide a differential gear mechanism of the locking differential type having a substantially reduced axial length.
It is a more specific object of the present invention to provide a locking differential in which the axial length is no more than would be required for a comparable open differential.
It is another object of the present invention to provide a locking differential mechanism which accomplishes the above-stated objects and in addition, has a minimum gear case diameter.
It is a more specific object of the present invention to provide a lockup mechanism (i.e., clutch set and cam mechanism), which makes it possible to minimize the distance from the actuating mechanism to the axis of rotation of the differential unit.
In prior art locking differentials of the type described above, wherein the cam mechanism includes one of the side gears, axial forces generated during the camming action are transmitted to the side gear, biasing it toward the opposite side gear. It has been necessary in such prior art locking differentials to provide some sort of thrust takeup device, such as a reaction block, between the side gears, to maintain the predetermined axial separation between the side gears, and prevent gear tooth wedging or splitting. Thus, the axial forces on the one side gear are transmitted to the opposite side gear and then to the casing, typically through a thrust washer. Such axial forces require, in addition to the reaction block, a sturdier casing, bolts, etc.
Accordingly, it is an object of the present invention to provide a differential gear mechanism of the locking differential type which substantially reduces the axial forces transmitted to the side gear during actuation of the lockup mechanism.
It is a more specific object of the present invention to provide a locking differential which achieves the above-stated object to the extent that no reaction block or other thrust member, other than the pinion gears, is required in order to maintain the axial separation between the side gears.